DESCRIPTION: The major focus of this proposal is to understand the mechanisms controlling the biological specificity of interleukin-9. The first specific aim will be to characterize the upstream and downstream signaling events mediated by interleukin-9. The role of IRS (insulin-receptor substrate) proteins in IL-9 signalling will be determined. This will be done by generating expression plasmids for overexpression and antisense expression of cDNAs for IRS proteins, generating dominate negative mutants for IRS proteins, and comparing the signaling events and biological effects of parental and transfected cell lines. IRS associated molecules will also be analyzed. The interaction of IL-9 receptor ligand-binding subunit, IRS proteins, and JAK1 will be studied by generating mutants of these proteins and studying the interaction of these molecules. The primary response genes activated by IL-9 will be identified and examined through differential display. Specific Aim 2 will determine the domains of the IL-9 receptor that connect the upstream and downstream signals and biological responses. This will largely be accomplished by mutagenesis studies of the IL-9 receptor and subsequent effects on ligand binding, signalling, and cellular responses.